This invention relates to high amylose content starch, in particular to a maize starch having an amylose content of more than 80% w/w. The invention further relates to single, double and multiple cross maize hybrids, particularly to a maize single cross F1 hybrid, capable of producing grain having such a high amylose content and to this grain.
The invention still further relates to fractions of high amylose starch that are enriched in dietary fibre and resistant starch content whilst claiming a high amylose content.
Most common starches contain approximately 25% amylose and 75% amylopectin. Amylose is a linear glucose polymer fraction, whilst amylopectin is a branched glucose polymer fraction.
In the prior art, it has been recognized that currently available commercial starch having an elevated amylose content would impart certain desirable properties to various compositions including films, foods and industrial products. Accordingly, attempts have been made in the prior art to produce high amylose content maize. This is exemplified in AU-A-45616/89 wherein a maize seed deposited as ATCC No. 40499 is disclosed as capable of yielding a starch having an amylose content of up to 72%.
Typically, however, a commercial starch having an amylose content of 55-65% would be regarded in the art as having a high amylose content.
The present inventors whilst recognizing the utility of the commercially available so-called high amylose starches, have sought to produce a maize having a still higher amylose content.
In the course of a breeding program, a single cross F1 hybrid maize seed was produced, which carried the ae amylose extender gene. This seed was found to be capable of producing grain, in which the amylose content of the starch derived therefrom was in excess of 80%.
Accordingly, in a first aspect, this invention consists in a hybrid maize seed capable of producing a starch having an amylose content of more than 80%.
In a second aspect, this invention further consists in a maize starch having an amylose content of more than 80%, physically or chemically modified derivatives thereof, and destructurized and non-destructurized forms thereof.
In a third aspect, this invention still further consists in compositions including a maize starch selected from the group consisting of maize starch having an amylose content of more than 80%, physically or chemically modified derivatives thereof and destructurized and non-destructurized forms thereof.
In a fourth aspect, this invention still further consists in a process for the formation of a composition comprising including a maize starch selected from the group consisting of maize starch having an amylose content of more than 80%, physically or chemically modified derivatives thereof and destructurized and non-destructurized forms thereof, in said composition.
In a fifth aspect, the present invention still further consists in a hybrid maize seed resulting from a cross between any of the parental lines selected from the group consisting of G112, G113, G116, G117, G118, G119W, G120, G121, G122, G125W, G126, G128, G129, G135W, G136W, G138W, G139W, G140W and G144, said hybrid maize seed yielding a starch having an amylose content of more than 80%.
Starch granules from any botanical source are a heterogeneous mixture varying in physiological age and this affects their physical size, structure and properties. If the starch granules are physically separated according to their granule size, it has been noted by a number of authors that the properties of each size fraction are somewhat different. For example, Cluskey et al in Starke, 32, 105-109(1980) reported on the fractionation of dent corn and amylomaize starch granules. They found that an inverse relationship existed between granule size and iodine binding capacity in the amylomaizes. Thus, the percent apparent amylose found in the fractions of amylose V starch amounted to 40% for the largest size particles and 52% for the smallest particles.
The correlation between amylose content and size fraction has been observed by the present inventors in relation to high amylose starches of the type mentioned above and in co-pending patent application PL6537.
In this latter mentioned patent application, PL6537, it was disclosed that high amylose starches have a high dietary fibre or resistant starch content. More specifically, it was found that there was a correlation between amylose content and dietary fibre/resistant starch such that increasing levels of amylose above 55% were associated with increasing levels of dietary fibre/resistant starch.
Patent application PL6537 further disclosed the useful nature of such starches in the preparation of food compositions having an enhanced dietary or resistant starch content.
Based on the observations of
(1) an association of dietary fibre and resistant starch with increasing levels of amylose; and
(2) increasing amylose content with decreasing starch granule size,
it was to be expected that decreasing starch granule size fractions of high amylose starch would be associated with enhanced levels of dietary fibre and resistant starch.
Surprisingly, this was found to be incorrect. In fact it was found that there is an optimum starch granule size fraction which is intermediate in size and not necessarily associated with the highest amylose content fraction.
Accordingly in a sixth aspect, the present invention still further consists in a starch fraction of enhanced dietary fibre and/or resistant starch content comprising a high amylose starch which has been fractionated according to granule size to yield a fraction which is characterised by a dietary fibre and/or resistant starch content which is greater than said high amylose starch.
In a seventh aspect, the present invention still further consists in a food composition having an enhanced dietary fibre and/or resistant starch content, including a starch fraction of enhanced dietary fibre and/or resistant starch content derived from a high amylose starch which has been fractionated according to granule size to yield a fraction which is characterised by a dietary fibre and/or resistant starch content which is greater than said high amylose starch.
For the purpose of the description of this invention, xe2x80x9chigh amylosexe2x80x9d means an amylose content (dsb) of 50% or more, preferably 70% or more, most preferably 80% or more. Particularly preferred amylose contents are 85% or more and 90% or more.
For the purposes of the description of the invention, the method by which amylose was determined is set out below.
METHOD: Apparent Amylose (Blue Value)
SCOPE: High Amylose Maize Starch
APPARATUS:
Defatting
Soxhlet extraction apparatus
Steam bath
Whatman thimbles, 25xc3x9780 mm
Drying Oven 105xc2x0 C.
Desiccator
Amylose Determination
Stoppered 50 ml test tubes
Vortex mixer
Boiling water bath
Spectrophotometer (605 mm, slit width 0.2 mm)
REAGENTS:
Defatting
Methanol (AR Grade)
Amylose Determination
Dimethylsulfoxide (HPLC Grade)
Iodine/Potassium iodide solution
3.0 g iodine and 30 g potassium iodide made up to 1000 mls with 0.1N sodium hydroxide
Methanol (AR Grade)
Amylose (Sigma Cat. No AO512)
Dried for 2 hours at 105xc2x0 C. prior to use.
PROCEDURE:
Defatting
(1) Weigh 5 grams of starch into the thimble.
(2) Place the thimble in the Soxhlet apparatus.
(3) Extract the sample with methanol (200 mls) for 20 hours
(4) Recover the thimble and dry in an oven at 105xc2x0 C. for 12 hours.
Amylose Determination
(1) Accurately weigh starch (100.0 to 105.0 mg) into the text tube.
(2) Add methanol (1 ml) and vortex mix.
(3) Add DMSO (15 mls), invert the test tube, and vortex mix.
(4) Place the test tubes in a vigorously boiling water bath for 60 minutes.
(5) Invert and vortex mix each test tube at 15 minute intervals during this period.
(6) Add distilled water (15 mls), invert and vortex mix. Place the test tube in the boiling water bath for a further 30 minutes.
(7) Quantitatively transfer the contents of the test tube to a 100 ml volumetric flask (use a funnel in the flask). Make the solution to volume with distilled water.
(8) Transfer an aliquot (3 mls) of this solution to a 100 ml volumetric flask and add 90 mls of distilled water.
(9) Add Iodine/Potassium Iodide solution (1 ml) to the diluted solution and immediately shake and mix thoroughly. Make to volume with distilled water.
(10) Measure the absorbance of this solution at 605 nm compared to a blank consisting of Iodine/Potassium Iodide solution (1 ml) diluted to 100 mls with distilled water in a volumetric flask.
CALCULATIONS:
For native starches:       %    ⁢          xe2x80x83        ⁢    Amylose    ⁢          xe2x80x83        ⁢    dsb    =                              Absorbance          xc3x97          13                                      wt            .                          xe2x80x83                        ⁢            sample                    ⁢                      xe2x80x83                    ⁢          dsb                    ⁢              
            *              xe2x80x83            ⁢      dsb        =          dry      ⁢              xe2x80x83            ⁢      solids      ⁢              xe2x80x83            ⁢              basis        .            
The method by which starch was separated from the maize grain was as follows:
1. Prepare 200 g meal by grinding through the 2 mm then the 1 mm screen of one Retsch Mill.
2. Wet thoroughly, stirring by hand, with 600 ml 0.1N NaOH.
3. Add 2,200 ml 0.1N NaOH and blend 5 minutes at ⅔ speed with the Ultra Turrax.
4. Sieve over 44 u screen.
5. Return sieve overs with 1 L water and blend for another 3 minutes, if necessary.
6. Sieve over 44 u screen.
7. Centrifuge filtrate at 3000 rpm for 15 minutes. Decant. Wipe out the neck of the bottle with a tissue to remove fat.
8. Reslurry starch (centrifugate) with 200 ml water, i.e. 50 ml in each of 4 tubes. Centrifuge.
9. Remove starch from centrifuge tubes with about 250 ml water.
10. Adjust pH of starch slurry to 6.0-6.5 with 0.5N HCl. Filter again over 44 u screen, if necessary.
11. Buchner filter and air dry.
In order to better understand the nature of this invention, a number of examples will be described.